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Contour plot of the exciton radius (variational parameter ) in a single finite quantum well for various well thicknesses and vertical electric fields.
Contour plots of (a) transition energy and (b) exciton binding energy in the Ge/SiGe quantum well system for the direct-gap e1-hh1 exciton. The shift is mainly dominated by the electric-field-dependent quantum well energy.
Contour plot of the optical oscillator strength for the direct-gap e1-hh1 transition in the Ge/SiGe quantum well system. It represents the absorption capability in a quantum well for QCSE electroabsorption modulation. The strength reduces with thicker well and higher vertical electric field.
Relative ratio of the direct-gap e1-hh1 absorption to the background absorption as a function of (a) vertical electric field and (b) well thickness. The background absorption is the indirect-gap absorption coefficient of Ge at the wavelength corresponding to the direct-gap transition energy. The ratio of 10 nm quantum well under zero field is normalized to 1. For the region where the direct-gap transition energy is lower than the indirect-gap energy, the background absorption issue does not exist.
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